Retinal prosthesis

ABSTRACT

The invention is a retinal prosthesis with an improved configuration mounting necessary components within and surrounding the eye. The present invention better allows for the implantation of electronics within the delicate eye structure. The invention further limits the necessary width of a thin film conductor passing through the sclera by use of a multiplexer external to the sclera and a demultiplexer internal to the sclera.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to a visual prosthesis andmore specifically to an improved mechanical and electricalconfigurations for retinal prosthesis for artificial vision.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to, and claims priority of, provisionalpatent application attorney docket S300-PRO Retinal Prosthesis.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the information as a sequence of electricalpulses which are relayed to the nervous system via the prostheticdevice. In this way, it is possible to provide artificial sensationsincluding vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, and avoid undue compression of thevisual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Humayun, U.S. Pat. No.5,935,155 describes the use of retinal tacks to attach a retinal arrayto the retina. Alternatively, an electrode array may be attached bymagnets or glue. U.S. Pat. No. 5,109,844 to de Juan describes a flatelectrode array placed against the retina for visual stimulation.

Any device for stimulating percepts in the retina must receive a signaldescribing a visual image along with power to operate the device. Thedevice can not be powered by wires as any connection through the skinwill create the risk of infection. Battery power is not practical asbatteries are bulky and surgery is required to replace them. Such signaland power may be transmitted into the eye inductively as shown inHumayun U.S. Pat. No. 5,935,155. Humayun uses a primary (external) coilin front of the eye, possibly encased within the rim of a pair ofglasses, and a secondary (internal) coil within the lens capsule oraround the sclera just under the conjunctiva. Implanting within the lenscapsule is difficult surgery and only allows for a small diameter coil.Larger coils are more efficient, can receive more power with lessresulting temperature rise per unit of power received. Implanting aroundthe sclera under the conjunctiva and near the surgical limbus (that isat the front of the eye) allows for a larger coil but may causeirritation or damage to the conjunctiva if the coil is placed in frontnear the cornea.

U.S. patent application Ser. No. 09/761,270, Ok, discloses several coilconfigurations including a configuration where the coil is offset about45 degrees from the front of the eye. The offset configuration allowsthe primary and secondary coils to be placed closer together allowingfor better inductive coupling. The bridge of nose partially blocksplacement of a primary coil when placed directly in front of the eye.

Vision simulations show that approximately 1000 pixels are needed toachieve basic visual functions such a face recognition and reading. Itwould be difficult or impossible to mount the electronics need for 1000pixels within the eye. Even if the electronics could be fit within theeye, heat dissipation would be a major issue. It would be equallydifficult to pass a cable capable of caring 1000 signal wires throughthe sclera. New mechanical and electrical configurations are needed tosupply such a high density electrode array.

SUMMARY OF THE INVENTION

The invention is a retinal prosthesis with an improved configurationmounting necessary components within and surrounding the eye. Thepresent invention better allows for the implantation of electronics,capable of high resolution display, within the delicate eye structure.The invention further limits the necessary width of a thin filmconductor passing through the sclera by use of a multiplexer external tothe sclera and a demultiplexer internal to the sclera.

Applicants have discovered that a coil and electronics package aroundthe sclera at or near 90 degrees rotation toward the lateral side of theeye has several advantages over previous designs. The secondary coilwill not irritate the conjunctiva as it is placed against the scleraunder the lateral rectus muscle, well behind the region where theconjunctiva attaches to the surgical limbus which is most susceptible toirritation. There is also more room between the conjunctiva and scleraon the side of the eye compared to the front of the eye. The primarycoil can be placed on the temples of a pair of glasses and/or hidden bythe user's hair. The spacing between primary and secondary coil can beas close, or closer, than that allowed for a coil pair located in thefront of the eye or at a 45 degree angle because there are no eyelids oreyelashes to interfere with the coil.

Such a side coil design, coil and electronics outside the eye anddemultiplexer inside the eye, facilitates the necessary space and heatdissipation needed for a high resolution video prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 depicts a retinal prosthesis with a secondary processing chip,including a demultiplexer, in the retina.

FIG. 3 depicts a retinal prosthesis with a secondary processing chip,including a demultiplexer, within the sclera but not on the retina.

FIG. 4 depicts a retinal prosthesis with a polymer thin film basedsecondary processor, including a demultiplexer, on the retina.

FIG. 5 depicts a retinal prosthesis with a polymer thin film basedsecondary processor, including a demultiplexer, within the sclera, butnot on the retina.

FIG. 6 is an external profile view of a user wearing the externalportion of the retinal prosthesis.

FIG. 7 is a description of the preferred demultiplexer and electrodechip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. An electrode array 10 is mounted by aretinal tack or similar means to the epiretinal surface. The electrodearray 10 is electrically coupled by a cable 12 which pierces the scleraand is electrically coupled to an electronics package 14, external tothe sclera. It is advantageous to encase the electronics within ahermetic package. This can be accomplished by use of a metal, ceramicpolymer or a combination of these materials case, or by applying a thinfilm hermetic coating such as described in U.S. patent application20020038134 Package for an Implantable Medical Device and 20020120296,Implantable Device Using Ultra-Nanocrystalline Diamond. An electronicspackage with a coil mounted on the lateral surface of the retina isdescribed in US patent application attorney docket S293-USA. All of theabove applications are incorporated herein by reference.

It is advantageous to mount electronics external to the sclera, as thefatty tissue there is less heat sensitive, and blood flow rapidlydissipates excess heat. The vitreous within the eye is does not changeoften and the retina is very heat sensitive.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil may be madefrom a thin film polymer sandwich with wire traces deposited betweenlayers of thin film polymer. The electronics package 14 and secondaryinductive coil 16 are held together by a molded body 18. The molded body18 may also include suture tabs 20. The molded body narrows to form astrap 22 which surrounds the sclera and holds the molded body 18,secondary inductive coil 16, and electronics package 14 in place. Themolded body 18, suture tabs 20 and strap 22 are preferably an integratedunit made of silicone elastomer. Silicone elastomer can be formed in apre-curved shape to match the curvature of a typical sclera. However,silicone remains flexible enough to accommodate implantation and toadapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap can better support an oval shaped coil.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. It is an advantage of the present design, that the entireimplanted portion of the prosthesis is attached to and supported by thesclera. By placing the device under the rectus muscles with theelectronics package in an area of fatty issue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

As we improve the resolution of retinal prostheses, the number ofelectrodes increases. As the number of electrodes increases the numberof wires between the electronics package and the electrode array mustincrease. This increase requires a wider thin film cable piercing thesclera. If the thin film cable is too wide, the sclerotomy may not healproperly. FIG. 2-5 present embodiments to provide for a narrower thinfilm cable between the electronics, external to the sclera, and theelectrode array within the sclera.

A common method of reducing the conductor count in cables, is the use ofa multiplexer and demultiplexer. However, multiplexers, like anyelectronic circuit, present unique problems when implanted within thehuman body. All electronics must be sealed to prevent the saline bodyfluids from harming the electronics and to prevent the electronics fromharming the body. Each electrical wire entering and exiting theelectronics package must also be sealed. Therefore it is advantageousthe limit the number of such wire electronics package interconnects.While it is easy to include a multiplexer within the electronicspackage, it is more difficult to house a demultiplexer within thesclera.

FIG. 2, depicts the preferred embodiment where a computer chip 110,including a demultiplexer is placed directly on the retina. Thedemultiplexer interconnects with the thin film cable 112 on one side andincludes electrode openings, for contacting the retina on the otherside. This is best accomplished by create feedthroughs in the siliconchip to allows electrodes on one side of the chip and connection to theflexible cable on the other side of the chip (described in more detailin FIG. 7. Cable 112 pierces the sclera and attaches to an electronicspackage 114. The electronics package connects to a coil 116. The chip110 must be coated with a thin film hermetic coating as described above.This is the simplest most cost effective method of providing ademultiplexer within the sclera.

Silicon chips such as chip 110 are necessarily flat. It is possiblethrough polishing to slightly curve one side, but the curvature islimited as the electrical circuit on the chip must be flat. It ispossible that chip 110 may be a series of silicon chips bonded to aflexible membrane to approximate the curvature of the retina. Thisallows for a larger electrode array than would be possible with a singlechip 110.

However, the retina is extremely delicate and can be damaged by eitherthe weight of such a demultiplexer chip or chips, or by the heatgenerated by the demultiplexer chip. If the chip can not be made lightenough or cool enough to attach to the sclera, other solutions areneeded.

FIG. 3, depicts an alternate embodiment where a demultiplexer chip 224is positioned within the eye, but not on the retina. Electrode array 210is connected to the demultiplexer 224 by a wide cable 226, anddemultiplexer 224 is connected to the electronics package 214 by anarrow cable 212. Narrow cable 212 pierces the sclera to attach to anelectronics package 214. The electronics package 214 also connects to acoil 216. This embodiment requires two interconnects on the externalelectronics package 214, one for the coil, and a low densityinterconnect to a cable piercing the sclera. This cable piercing thesclera is connected to another low density interconnect on thedemultiplexer chip within the sclera. Finally there must be a highdensity interconnect on the demultiplexer connected to a thin filmelectrode array. While this solution is more complex, it moves theweight and heat of the demultiplexer off the retina.

FIG. 4, depicts yet another embodiment where the demultiplexer is not asilicon based integrated circuit, but an integrated circuit depositeddirectly on the thin film electrode array 310. The demultiplexerinterconnects with the thin film cable 312 on one side and includeselectrode openings, for contacting the retina on the other side. Cable312 pierces the sclera and attaches to an electronics package 314. Theelectronics package connects to a coil 316. Several integrated circuitmanufacturers are building integrated circuits on Mylar thin films. Thesame technique can be used to build integrated circuits on polyimide orother biocompatible thin film polymers. By depositing the demultiplexercircuitry directly on the thin film, one avoids the weight of a siliconbased integrated circuit and the possible damage to the retina cause bythe weight of a silicon based demultiplexer. Further, building thedemultiplexer circuit directly on the thin films avoids the need for ahermetic interconnection to a demultiplexer chip or a hermetic coatingon the chip. If the heat output of a thin film based demultiplexer issufficiently small, the demultiplexer can be built directly into theelectrode array, completely eliminating the need for a thin film wideenough to include one connector for each electrode.

If the heat output of a thin film demultiplexer is likely to causedamage to the retina, another embodiment, shown in FIG. 5, provides athin film demultiplexer between the electrode array and electronicspackage, but sufficiently distant from the retina, to avoid heat damage.FIG. 5, depicts an alternate embodiment where a thin film demultiplexer424 is positioned within the eye, but not on the retina. Electrode array410 is connected to the demultiplexer 424 by a wide cable 426, anddemultiplexer 424 is connected to the electronics package 414 by anarrow cable 412. Narrow cable 412 pierces the sclera to attach to anelectronics package 414. The electronics package 414 connects to a coil416. It is possible to form the electrode 410, wide cable, 426,demultiplexer 424, and thin cable 412 on a single thin film substrate.While this solution is more complex, it moves the heat of thedemultiplexer off the retina.

FIG. 6 depicts the profile of a user wearing the external portion of theretinal prosthesis. The entire device may be built into the temple of apair of glasses. A camera 530 collects a video image and transmits datato an external electronics package 532. A battery 534 powers the camera530, external electronics package 532, and provides power to a primaryinductive coil 536. The primary inductive coil 536 sends power and datathrough the skin and skull to the secondary inductive coil 16. Maximumefficiency is obtained when the primary inductive coil 536 and secondaryinductive coil 16 are the same size, shape and as close together aspossible.

FIG. 7, depicts the preferred demultiplexer chip 110. A siliconsubstrate 610 has a demultiplexer 612 applied by conventional means.Micromachining techniques are used to create voids in the siliconsubstrate 610, which are filled with conductive feedthroughs 616.Electrodes 614, for contact with the retina, are applied to theconductive feedthroughs 616 by electroplating or other means. A thinfilm hermetic coating 618 is applied to the silicon substrate 610allowing voids for electrodes 614 and contacts 620. Finally a thin filmcable 622 is attached to the contacts 620 to supply power and signal tothe demultiplexer chip.

Accordingly, what has been shown is an improved retinal prosthesis.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is therefore tobe understood that within the scope of the claims, the invention may bepracticed otherwise than as specifically described herein.

1. A retinal prosthesis comprising: An electrode array suitable to be mounted in close proximity to a retina; A demultiplexer electrically coupled to said electrode array; and An implantable electronics package, including a multiplexer, electrically coupled to said demultiplexer.
 2. The retinal prosthesis according to claim 1, wherein said electronics package is in a hermetic package.
 3. The retinal prosthesis according to claim 1, wherein said demultiplexer is suitable to be mounted within the eye, but distant from the retina.
 4. The retinal prosthesis according to claim 1, wherein said demultiplexer is on a silicon chip.
 5. The retinal prosthesis according to claim 4, wherein said silicon chip is attached to a thin film cable.
 6. The retinal prosthesis according to claim 4, wherein said silicon chip is enclosed within a hermetic package.
 7. The retinal prosthesis according to claim 6, wherein said hermetic package is a hermetic case.
 8. The retinal prosthesis according to claim 6, wherein said hermetic package is a thin film hermetic coating.
 9. The retinal prosthesis according to claim 1, wherein said electrode array and said demultiplexer are formed on a common substrate.
 10. The retinal prosthesis according to claim 9, wherein said common substrate is a silicon chip.
 11. The retinal prosthesis according to claim 10, wherein said silicon chip includes electrodes on a first side and electrical contacts for a cable on a side opposite said first side.
 12. The retinal prosthesis according to claim 11, further comprising conductive feedthroughs in said silicon chip.
 13. The retinal prosthesis according to claim 1, wherein said electronics package is suitable to be mounted external to the sclera, but supported by the sclera.
 14. The retinal prosthesis according to claim 13, wherein said electronics package is mounted lateral to the sclera.
 15. The retinal prosthesis according to claim 1, wherein said multiplexer is said side opposite of said first side.
 16. The retinal prosthesis according to claim 1, wherein said electronics package is coupled to a implantable coil.
 17. The retinal prosthesis according to claim 1, wherein said multiplexer is deposited on a thin film substrate.
 18. The retinal prosthesis according to claim 1, wherein said electrode array and said multiplexer are deposited on a common thin film substrate.
 19. A retinal prosthesis comprising: An electrode array suitable to be mounted in close proximity to a retina; A demultiplexer suitable to be mounted internal to the sclera; An electronics package suitable to be mounted within the eye and supported by the sclera; A first cable electrically coupling said electrode array to said demultiplexer; A second cable electrically coupling said demultiplexer to said electronics package; and An implantable coil electrically coupled to said electronics package.
 20. The retinal prosthesis according to claim 19, wherein said demultiplexer is suitable to be mounted within the eye, but distant from the retina.
 21. The retinal prosthesis according to claim 19, wherein said demultiplexer is on a silicon chip.
 22. The retinal prosthesis according to claim 19, wherein said electrode array and said demultiplexer are formed on a common substrate.
 23. The retinal prosthesis according to claim 19, wherein said common substrate is a silicon chip.
 24. The retinal prosthesis according to claim 23, wherein said silicon chip is attached to a thin film cable.
 25. The retinal prosthesis according to claim 23, wherein said silicon chip includes electrodes on a first side and electrical contacts for a cable on a side opposite said first side.
 26. The retinal prosthesis according to claim 25, further comprising conductive feedthroughs in said silicon chip.
 27. The retinal prosthesis according to claim 19, wherein said multiplexer is deposited on a thin film substrate.
 28. The retinal prosthesis according to claim 19, wherein said electrode array and said multiplexer are deposited on a common thin film substrate.
 29. The retinal prosthesis according to claim 19, wherein said electrode array, said multiplexer, said first cable and said second cable are deposited on a common thin film substrate.
 30. A retinal prosthesis comprising: A camera for collecting a video image; A video processor coupled to said camera for processing said video image; A primary coil coupled to said video processor for transmitting said video image into a body; An secondary coil suitable to be implanted within the body but external to a sclera for receiving said video image; An electronics package, electrically coupled to said secondary coil, suitable to be mounted external to the sclera and supported by the sclera; A demultiplexer suitable to be mounted internal to the sclera; An electrode array suitable to be mounted in close proximity to a retina; A first cable electrically coupling said electrode array to said demultiplexer; A second cable electrically coupling said demultiplexer to said electronics package; and A second cable electrically coupling said demultiplexer to said electronics package.
 31. The retinal prosthesis according to claim 18, wherein said demultiplexer is a silicon chip.
 32. The retinal prosthesis according to claim 19, wherein said silicon chip is within a hermetic package. 